The objectives are to study the development of sustained, endogenous attention in young infants, and to relate developmental trends in sustained attention to concurrent heart rate (HR) and respiration. The specific aims are 1) to study sustained, subject-controlled attention in infants from two to six months of age, and to study sustained attention in preterm infants, 2) to relate resting measurements of HR, respiration, and respiratory sinus arrhythmia (RSA) to visual, cardiac, and respiration responses occurring during infant visual attention, and 3) to determine how HR and respiration responses are related to visual attention in young infants, and to extend the study of sustained attention to include other aspects of HR-defined visual information processing phases. The research may provide a "model preparation" for the study of pathological patterns of attention found in hyperactive, autistic, and retarded children, and could lead to the early diagnosis of children who are "at-risk" for poor intellectual outcome. Infants at 14, 20, and 26 weeks of age (30 per age) will be tested. HR and respiration will be measured during a 5 min baseline and during attention. Experiment 1 will test the relative efficacy for recognition memory performance of the interrupted stimulus, infant control, and accumulated looking time methods of visual stimulus presentation. In Experiment 2, preterm infants will be tested in a longitudinal design, to determine if intra-individual patterns of development of RSA parallel the expected pathological patterns of sustained attention. In Experiment 3, infants ability to detect the presence of a peripheral stimulus will be tested during heartrate-defined phases of processing of visual stimulus. Experiment 4 will examine the acquisition of recognition memory during HR define attention phases, by presenting a "to-be- remembered" visual stimulus during specific phases. The existence of a refractory period following the termination of visual attention will be examined in Experiment 5. Experiment 6 will examine peripheral stimulus detection during the refractory period following attention termination, in order to test the behavioral consequences of the hypothesized refractory period. It is predicted that 1) sustained attention will show the largest age- related changes of the HR-defined attention phases, and 2) the developmental increase in sustained attention will parallel developmental changes in baseline RSA, and concurrent HR and respiration.